Multilayer diffusion barrier for copper interconnections

ABSTRACT

It is a general object of the present invention to provide an improved method of fabrication in the formation of an improved copper metal diffusion barrier layer having the structure, W/WSiN/WN, in single and dual damascene interconnect trench/contact via processing with 0.10 micron nodes for MOSFET and CMOS applications. The diffusion barrier is formed by depositing a tungsten nitride bottom layer, followed by an in situ SiH 4 /NH 3  or SiH 4 /H 2  soak forming a WSiN layer, and depositing a final top layer of tungsten. This invention is used to manufacture reliable metal interconnects and contact vias in the fabrication of MOSFET and CMOS devices for both logic and memory applications and the copper diffusion barrier formed, W/WSiN/WN, passes a stringent barrier thermal reliability test at 400° C. Pure single barrier layers, i.e., single layer WN, exhibit copper punch through or copper spiking during the stringent barrier thermal reliability test at 400° C.

DOMESTIC PRIORITY CLAIM

This application is a divisional of U.S. patent application Ser. No.09/587,465 filed Jun. 5, 2000, and entitled, “Method of FormingMultilayer Diffusion Barrier for Copper Interconnections,” which ishereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates to a method of fabrication in the formation of animproved copper metal diffusion barrier layer, W/WSiN/WN, by acombination of a tungsten nitride bottom layer, followed by an in situsilane soak process forming a WSiN layer, and a final top layer oftungsten, in single and dual damascene interconnect trench/contact viaprocessing with 0.10 micron nodes for MOSFET and CMOS applications.

(2) Description of Related Art

Related patents and relevant literature now follow as Prior Art.

U.S. Pat. No. 6,001,415 entitled “Via With Barrier Layer for ImpedingDiffusion of Conductive Material from Via Into Insulator” granted Dec.14, 1999 to Nogami et al. describes a method of forming variousdiffusion barrier layers, i.e., both pure WSiN and pure WN barrierlayers, for conducting copper contact vias. The via structure describedincludes a barrier layer disposed between a via plug and an insulatinglayer surrounding a via hole to impede diffusion of conductive materialfrom the via plug into the insulating layer. The deposition of thebarrier metals described use an ion metal plasma sputtering process thatis combined with a plasma etching process to remove unwanted barrierlayer material from the bottom of the contact via.

U.S. Pat. No. 5,801,098 entitled “Method of Decreasing Resistivity in anElectrically Conductive Layer” granted Sep. 1, 1998 to Fiordalice et al.describes a method of decreasing resistivity in an electricallyconductive, diffusion barrier layer of TiN, that includes the use of ahigh density plasma sputtering technique to deposit the electricallyconductive TiN layer. The electrically conductive diffusion barrierlayer is further exposed to a plasma anneal.

U.S. Pat. No. 5,968,333 entitled “Method of Electroplating a Copper orCopper Alloy Interconnect” granted Oct. 19, 1999 to Nogami et al.describes a process whereby copper or a copper alloy is electroplated tofill via/contact holes and/or trenches in a dielectric layer. A barrierlayer is initially deposited on the dielectric layer lining thehole/trench. A thin conformal layer of copper or a copper alloy issputter deposited on the barrier layer outside the hole/trench. Copperor a copper alloy is then electroplated on the conformal copper orcopper alloy layer filling the hole/trench. During electroplating, thebarrier layer functions as a seed layer within the hole/trench. Thebarrier layer materials include single layers of: W, WN, WSiN, TiN,TiSiN and TiW.

U.S. Pat. No. 5,907,188 entitled “Semiconductor Device with ConductiveOxidation Preventing Film and Method for Manufacturing the Same” grantedMay 25, 1999 to Nakajima et al. describes a semiconductor device thatincludes a semiconductor substrate, and a laminated film insulativelyformed over the semiconductor substrate. A conductive oxidationpreventing film is disposed between a refractory metal film and asemiconductor film, to prevent oxidation of the semiconductor film.Oxidation and diffusion barriers, i.e., single layers of W, WN, andWSiN, are mentioned in the specifications.

U.S. Pat. No. 5,985,762 entitled “Method of Forming a Self-AlignedCopper Diffusion Barrier in Vias” granted Nov. 16, 1999 to Geffken etal. describes a process whereby a copper diffusion barrier is formed onthe side walls of vias connected to copper conductors, to prevent copperdiffusion into inter-level dielectric. A thin film of copper diffusionbarrier material is deposited on the wafer post via etch. A sputter etchis performed to remove barrier material from the base of via and toremove copper oxide from the copper conductor. The barrier material isnot removed from the sidewall during the sputter etch. Thus, a barrierto re-deposited copper is formed on the via sidewalls to prevent copperpoisoning of the dielectric. Barrier materials that are mentionedinclude single layers of: Ta, TiN, Si₃N₄, TaN, WN, WSiN, and TaSiN.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide an improvedmethod of fabrication in the formation of an improved copper metaldiffusion barrier layer having the structure, W/WSiN/WN, in single anddual damascene interconnect trench/contact via processing with 0.10micron nodes for MOSFET and CMOS applications. The diffusion barrier isformed by depositing a tungsten nitride bottom layer, followed by an insitu SiH₄/NH₃ or SiH₄/H₂ soak forming a WSiN layer, and depositing afinal top layer of tungsten. This invention is used to manufacturereliable metal interconnects and contact vias in the fabrication ofMOSFET and CMOS devices for both logic and memory applications and thecopper diffusion barrier formed, W/WSiN/WN, passes a stringent barrierthermal reliability test at 400° C. Pure single barrier layers, i.e.,single layer WN, exhibit copper punch through or copper spiking duringthe stringent barrier thermal reliability test at 400° C.

In summary of the present invention, a process flow description followsthat summarizes the necessary process steps and sequence of stepsnecessary for the main embodiments of the present invention, to formW/WSiN/WN barrier layer, which exhibits high diffusion resistance toboth copper and silicon (at both interfaces). The necessary processsteps and sequence of steps necessary to form the W/WSiN/WN areoutlined, as follows. Step one is the deposition of the WN film or layerin the trench/via opening by metal-organic chemical vapor deposition(MOCVD) from the reduction of tungsten organic precursors, or depositedby plasma-enhanced chemical vapor deposition (PECVD), or by physicalvapor deposition (PVD), sputtering. Step two in the process flowdescription is the an in situ soak process treating the WN layer with aSiH₄/NH₃ gas mixture or a SiH₄/H₂ gas mixture, at between from about 300to 400° C. This reactive soak process forms a WSiN layer on top of theWN layer, thus a WSiN/WN barrier. Following the silane soak treatment,is step three, the final top barrier deposition by chemical vapordeposition (CVD) or physical vapor deposition (PVD), sputtering, of atungsten layer. Thus, a W/WSiN/WN barrier layer is formed. Next, stepfour is the copper seed layer deposition with improved adhesion andcopper crystal texture, preferred dense <111>, upon the rigid diffusionthe barrier layer, W/WSiN/WN. This fine crystal texture is important forsubsequent electrochemical deposition (ECD) of copper, whichsubsequently fills the trench/via cavity. The copper seed layer,deposited over the tungsten layer, exhibits fine, highly dense grains,as studied by scanning electron microscopy (SEM). The subsequent processstep, the electrochemical deposition (ECD) of copper, is used to fillthe trench cavity, upon the copper seed layer. The kinetics of theelectrochemical copper deposition process are based on a uniform,defect-free seed layer and barrier layer with good adhesion properties.The underlying layers improve and make wider the process window for thedeposition of copper to fill both single and dual damascene structures.

The final processing step in building of the single and dual damascenestructure is the chemical mechanical polishing (CMP) back of the excesselectrochemical deposited copper metal. The copper is chem-mech polishedback without dishing. In addition, any excess seed layer and barrierlayer are removed from the top substrate surface. The copper is polishedback so that only the copper that lies in the openings is left to formsingle and dual inlaid structures that include via and interconnectportions. Device applications include MOSFET and CMOS devices.

This invention has been summarized above and described with reference tothe preferred embodiments. Some processing details have been omitted andare understood by those skilled in the art. More details of thisinvention are stated in the “DESCRIPTION OF THE PREFERRED EMBODIMENTS”section.

BRIEF DESCRIPTION OF THE DRAWINGS

The object and other advantages of this invention are best described inthe preferred embodiments with reference to the attached drawings thatinclude:

FIG. 1, which in cross-sectional representation illustrates a trenchstructure filled with the first layer of the copper metal barrier layer,WN, deposited by metal-organic chemical vapor deposition (MOCVD) fromthe reduction of tungsten organic precursors, or deposited byplasma-enhanced chemical vapor deposition (PECVD), or by physical vapordeposition (PVD), sputtering.

FIG. 2, which in cross-sectional representation illustrates the in situsoak process treating the WN layer with an in situ SiH₄/NH₃ or SiH₄/H₂soak at between 300 and 400° C. forming a WSiN layer on top of the WNlayer, thus WSiN/WN barrier.

FIG. 3, which in cross-sectional representation illustrates the finaltop barrier deposition by chemical vapor deposition (CVD) or physicalvapor deposition (PVD), sputtering, of tungsten, thus forming W/WSiN/WNbarrier layer.

FIG. 4, which in cross-sectional representation illustrates anotherembodiment of the present invention, the copper seed layer with improvedadhesion and copper crystal texture, upon the rigid diffusion thebarrier layer, W/WSiN/WN, for subsequent electrochemical deposition(ECD) of copper to fill the trench/via cavity.

FIG. 5, includes a process flow diagram summarizes the necessary processsteps and sequence of steps necessary for an embodiment of the presentinvention, to form W/WSiN/WN barrier layer, which exhibits highdiffusion resistance to both copper and silicon (at both interfaces).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is a general object of the present invention to provide an improvedmethod of fabrication in the formation of an improved copper metaldiffusion barrier layer having the structure, W/WSiN/WN, in single anddual damascene interconnect trench/contact via processing with 0.10micron nodes for MOSFET and CMOS applications. The diffusion barrier isformed by depositing a tungsten nitride bottom layer, followed by an insitu SiH₄/NH₃ or SiH₄/H₂ soak forming a WSiN layer, and depositing afinal top layer of tungsten. This invention is used to manufacturereliable metal interconnects and contact vias in the fabrication ofMOSFET and CMOS devices for both logic and memory applications and thecopper diffusion barrier formed, W/WSiN/WN, passes a stringent barrierthermal reliability test at 400° C. Pure single barrier layers, i.e.,single layer WN, exhibit copper punch through or copper spiking duringthe stringent barrier thermal reliability test at 400° C.

It has been found that one reason that just a WN layer alone does notwork, as well as, a W/WSiN/WN composite barrier layer is the possibilityof pin holes in the WN layer. Pin holes facilitate the movement (throughfast surface diffusion) of copper through the WN layer, duringsubsequent thermal processing, resulting in copper spiking or punchthrough of the barrier.

Referring to FIG. 1 illustrated in cross-sectional drawing, forcompleteness provided by the present invention, is a semiconductorsubstrate 10 with an insulating layer 12. A copper metal interconnect 16is patterned within an insulating layer 14. In addition, a layer of lowdielectric constant material 17 is deposited and patterned into a trench18 (gap) opening in FIG. 1. Provided is a single damascene structure 18and/or a dual damascene structure (not shown in Figs.). The typicalinsulator material is silicon oxide type compounds. Also, polysilicongate structures (with silicides) and source/drain diffusions aretypically upon or in a single crystal silicon substrate or IC module(not shown in figures).

Referring again in more detail to FIG. 1, which is a cross-sectionalrepresentation shows the first embodiment of the present invention, atrench structure filled with the first layer of the copper metal barrierlayer, WN (19), deposited by metal-organic chemical vapor deposition(MOCVD) from the reduction of tungsten organic precursors, or depositedby plasma-enhanced chemical vapor deposition (PECVD), or by physicalvapor deposition (PVD), sputtering.

Referring to FIG. 2, which in cross-sectional representation illustratesone of the main embodiments of the current invention, an in situ soakprocess treating the WN layer (19) with a SiH₄/NH₃ gas mixture (20) or aSiH₄/H₂ gas mixture (20), at between from about 300 to 400° C. Thisreactive soak process forms a WSiN layer (22) on top of the WN layer(19), thus forming a WSiN/WN barrier. Silicon atoms diffuse between thegains and into the grain boundaries of the WN film. Therefore, thesilicon atoms block the diffusion path of deleterious copper atoms.

Referring to FIG. 3, illustrated in cross-sectional drawing is shown theresult of the main embodiments of the current invention, the final topbarrier deposition by chemical vapor deposition (CVD) or physical vapordeposition (PVD), sputtering, of tungsten (30). Thus, a W/WSiN/WNbarrier layer is formed. The top tungsten barrier layer (30) isdeposited over the WSiN layer (22) and the bottom WN layer (19). Thistop tungsten barrier layer yields better copper seed layer properties inthe next process step.

FIG. 4, which in cross-sectional representation illustrates anotherembodiment of the present invention, the copper seed layer (40)deposition with improved adhesion and copper crystal texture, preferreddense <111>, upon the rigid diffusion the barrier layer, W/WSiN/WN. Thisfine crystal texture is important for subsequent electrochemicaldeposition (ECD) of copper, which subsequently fills the trench/viacavity. The copper seed layer (40) deposited over the tungsten layer(30) exhibits fine, highly dense grains, as studied by scanning electronmicroscopy (SEM). 9. The trench or channel and the via hole contact islined with the adhesive copper seed layer on the diffusion barrierlayer. The copper seed layer can be deposited by several methods:electrochemical deposition (ECD), or by physical vapor deposition (PVD)sputtering, and the seed layer material is comprised of a copper metallayer, thickness from about 1,000 to 2,200 Angstroms by PVD, andthickness from about 200 to 500 Angstroms by chemical vapor deposition(CVD).

FIG. 5, includes a process flow diagram summarizes the necessary processsteps and sequence of steps necessary for an embodiment of the presentinvention, to form W/WSiN/WN barrier layer, which exhibits highdiffusion resistance to both copper and silicon (at both interfaces).The necessary process steps and sequence of steps necessary to form theW/WSiN/WN are outlined in FIG. 5. Step one (1) is the deposition of theWN film or layer in the trench/via opening by metal-organic chemicalvapor deposition (MOCVD) from the reduction of tungsten organicprecursors, or deposited by plasma-enhanced chemical vapor deposition(PECVD), or by physical vapor deposition (PVD), reactive sputtering.Step two (2) in the flow diagram is the an in situ soak process treatingthe WN layer with a SiH₄/NH₃ gas mixture or a SiH₄/H₂ gas mixture, atbetween from about 300 to 400° C. This reactive soak process forms aWSiN layer on top of the WN layer, thus a WSiN/WN barrier. Following thesilane soak treatment, is step three (3), the final top barrierdeposition by chemical vapor deposition (CVD) or physical vapordeposition (PVD), sputtering, of a tungsten layer. Thus, a W/WSiN/WNbarrier layer is formed. Next, step four (4) is the copper seed layerdeposition with improved adhesion and copper crystal texture, preferreddense <111>, upon the rigid diffusion the barrier layer, W/WSiN/WN. Thisfine crystal texture is important for subsequent electrochemicaldeposition (ECD) of copper, which subsequently fills the trench/viacavity. The copper seed layer, deposited over the tungsten layer,exhibits fine, highly dense grains, as studied by scanning electronmicroscopy (SEM). Not shown in the Figs., is the subsequent processstep, the electrochemical deposition (ECD) of copper, used to fill thetrench cavity, upon the copper seed layer. The kinetics of theelectrochemical copper deposition process are based on a uniform,defect-free seed layer and barrier layer with good adhesion properties.The underlying layers improve and make wider the process window for thedeposition of copper to fill both single and dual damascene structures.

The final processing step in building of the single and dual damascenestructure is the chemical mechanical polishing (CMP) back of the excesselectrochemical deposited copper metal. The copper is chem-mech polishedback without dishing. In addition, any excess seed layer and barrierlayer are removed from the top substrate surface. The copper is polishedback so that only the copper that lies in the openings is left to formsingle and dual inlaid structures that include via and interconnectportions. Device applications include MOSFET and CMOS devices. Robustdiffusion barriers are critical to these technologies since copper is anexcellent mid-band gap, recombination center in semiconductor materialand minor carrier lifetime, retention time, is severely reduced bycopper contamination in the semiconductor device regions.

Some of the process details and specifications for the in situ soakprocess, are as follows. The in situ soak process treats the WN layerwith a SiH₄/NH₃ gas mixture or a SiH₄/H₂ gas mixture, at between fromabout 300 to 400° C. This reactive soak process forms a WSiN layer ontop of the WN layer, thus forming a WSiN/WN barrier. Gas pressure rangesfrom about 1 to 10 Torr. Gas flows are, with a SiH₄/NH₃ gas mixture,SiH₄ gas flow from about 40 to 60 sccm and NH₃ gas flow from about 5 to10 sccm. Gas flows are, with a SiH₄/H₂ gas mixture, SiH₄ gas flow fromabout 40 to 60 sccm and H₂ gas flow from about 2 to 3 sccm. Reactiontime at processing temperature ranges from about 6 to 60 seconds. TheWSiN layer thickness, formed by the above process, is from approximately30 to 60 Angstroms. (Note, the in situ soak process that treats the WNlayer, as specified above, is intentionally not a plasma process.)

Some of the specifications for the sandwich barrier structure or barrierlayer W/WSiN/WN, are as follows. For a 300 Angstrom barrier layer ofW/WSiN/WN, W thickness is approximately 40 Angstroms, WSiN thickness isfrom approximately 30 to 60 Angstroms, and WN thickness is approximately200 Angstroms. If the total barrier layer W/WSiN/WN thickness is made tobe thicker or thinner than 300 Angstroms, this has the effect of eitherincreasing or decreasing only the WN thickness, as shown in thefollowing example. For example, for a total barrier layer W/WSiN/WNthickness of 200 Angstroms, the W thickness is still approximately 40Angstroms, WSiN thickness is still from approximately 30 to 60Angstroms, but the affected WN thickness is now approximately 100Angstroms. In general terms, the trench or channel and via hole contactis lined with a diffusion barrier layer comprised of a composite barrierwith top layer of W thickness from about 30 to 50 Angstroms, interposedor intervening layer of WSiN thickness from about 30 to 60 Angstroms,and bottom layer of WN thickness from about 60 to 400 Angstroms.

One process variation or process option of the present invention, is asfollows. The tungsten layer of the W/WSiN/WN barrier layer can beomitted to form a WSiN/WN barrier layer. Omitting the tungsten layer andthe associated processing to deposit that layer, has the followingaffects on the barrier layer properties. Comparing the top of thebarrier layer, W versus WSiN, W has a better crystal texture than WSiN.More specifically, WSiN is an amorphous phase or “nano-crystalline”phase (very small crystals or grains, close to amorphous). Theproperties of the conducting copper metal, that is deposited upon thebarrier layer, are dependent upon the barrier layer material that is onthe top surface of the barrier layer. A specific example of this barrierlayer surface affect on the deposited copper layer properties is asfollows. A barrier layer with W on top has the following properties: thetungsten layer has a better grain or crystal texture (finer texture)than a top layer of WSiN layer. Furthermore, the if copper is directlydeposited on a layer of WSiN, the copper grains exhibit less of thedesirable preferred crystal orientation <111>/<200>. However, the ifcopper is directly deposited on a layer of W, the copper grains exhibitmore of the desirable preferred crystal orientation <111>/<200>. Thiseffect is attributed to the better crystal texture of the tungstenlayer. In cases where the process variation or process option ofomitting the W top layer is exercised, the trench or channel and viahole contact is lined with a diffusion barrier layer comprised of acomposite barrier with a top layer of WSiN thickness from about 30 to 60Angstroms, and a bottom layer of WN thickness from about 60 to 400Angstroms.

While the invention has been particularly shown and described withreference to the preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade without departing from the spirit and scope of the invention.

1. An integrated circuit comprising: a semiconductor substrate; apatterned insulating dielectric layer disposed over the substrate,wherein the patterned insulating dielectric layer includes a dual inlaidopening over an underlying interconnect; a WN first diffusion barrierlayer disposed over the patterned insulating dielectric layer and linesthe opening; a WSiN second diffusion barrier layer disposed over the WNfirst diffusion barrier layer; a copper seed layer disposed over theWSiN second diffusion barrier layer; and a copper conducting layerdisposed over the thin copper seed layer.
 2. The circuit of claim 1,wherein the dual inlaid opening comprises a trench/via cavity and the WNfirst diffusion barrier layer, WSiN second diffusion barrier layer,copper seed layer, and copper conducting layers forms a trench/via linerin small dimensional node applications of approximately 0.1 microns. 3.The circuit of claim 1, wherein the WN first diffusion barrier layer hasa thickness ranging from about 60 to about 400 Angstroms, and the WSiNsecond diffusion barrier layer has a thickness ranging from about 30 toabout 60 Angstroms.
 4. The circuit of claim 1, wherein the copper seedlayer has a thickness ranging from about 200 to about 2,200 Angstroms.5. The circuit of claim 1, wherein the copper conducting layer formsconducting interconnect lines and contact vias.
 6. The circuit of claim1, further comprising a W third diffusion barrier layer disposed overthe WSiN second diffusion barrier layer and below the copper seed layer.7. A diffusion barrier structure formed in the fabrication of anintegrated circuit comprising: a semiconductor substrate; a patternedinsulating dielectric layer disposed over the substrate, wherein thepatterned insulating dielectric layer includes an opening disposed overan underlying interconnect; a WN first diffusion barrier layer disposedover the patterned insulating dielectric layer and lines the opening; aWSiN second diffusion barrier layer disposed over the WN first diffusionbarrier layer; and a W third diffusion barrier layer disposed over theWSiN second diffusion barrier layer.
 8. The structure of claim 7,wherein the opening comprises a trench/via cavity and the WN firstdiffusion barrier layer, WSiN second diffusion barrier layer, copperseed layer, and copper conducting layers forms a trench/via liner insmall dimensional node applications of approximately 0.1 microns.
 9. Thestructure of claim 7, wherein the WN first diffusion barrier layer has athickness ranging from about 60 to about 400 Angstroms, and the WSiNsecond diffusion barrier layer has a thickness ranging from about 30 toabout 60 Angstroms, and W third diffusion barrier layer has a thicknessranging from about 30 to about 50 Angstroms.
 10. The structure of claim7, further comprising an adhesive copper seed layer disposed over the Wthird diffusion barrier layer.
 11. The structure of claim 10, whereinthe adhesive copper seed layer has a thickness ranging from about 200 toabout 2,200 Angstroms.
 12. The structure of claim 10, further comprisinga copper layer disposed over the copper seed layer forming conductinginterconnect lines and contact vias.